1. Field of the Invention
The present invention relates to a control plate for use in a gas discharge display device having a matrix formed of perpendicular row and column conductor tracks on opposite sides of the plate with perforations through the plate at points of intersection of the rows and columns, and in particular to such a control plate wherein the metallization of the row and columns extends a distance into the perforations to prevent accumulation of charge therein.
2. Description of the Prior Art
Control plates for gas discharge display devices which essentially divide the interior of the display device into two portions are known in the art which have metallized row conductor tracks on one side and metallized column conductor tracks on the other side. The conductor and column tracks are disposed perpendicularly with respect to each other and in combination form a matrix having perforations through the control plate at the points of intersection of the row and column tracks. By selectively energizing a row conductor track and a column conductor track, the control perforation at the point of intersection of the energized row and column is thus also energized. Electrons in the plasma of the gas discharge space lying behind the control plate are thereby attracted into the acceleration space disposed in front of the control plate and are accelerated in this space onto the anode. An image point of light corresponding to the selected point of intersection of the matrix thereby arises at the point of incidence of the electron on a luminescent screen situated in front of the anode. Characters and images can be displayed on the luminescent screen by the utilization of an appropriate matrix drive circuit which controls the sequence and strength of the images. Such a display device functions according to the general principles of spacial separation of electron generation and electron acceleration, the so called double chamber principle, and is known, for example, from German OS No. 24 12 869 corresponding to U.S. Pat. No. 3,956,662 as well as German OS No. 26 15 721, corresponding to U.S. Pat. No. 4,112,329, the teachings of which are incorporated herein by reference.
As described above, the control plate in devices of the type found in the prior art consists of a carrier plate comprised of electrically insulating material such as, for example, glass, with metallized electrode tracks deposited on the opposite sides of the plate. In the conventional manufacture of such control plates, the perforation structure required for the electron passage through the plate is not etched into the glass until after the application of the track conductors on the front and rear sides of the plate perpendicular to each other. In order to achieve a high resolution of the image to be displayed on the luminescent screen, a very fine grid pattern is required consisting of the row and column conductors. The perforation structure which operates in combination with the grid structure can be etched in the carrier plate only if the carrier plate is comprised of a very thin glass plate as a result of etching technology limitations known to those skilled in the art. Such a thin glass plate has low mechanical stability and is subject to fracture which of course requires replacement of the plate before operation of the gas discharge device can resume, and in some cases in which the plate cannot be replaced renders the entire device useless.
This problem has resulted in the utilization of thicker carrier plates which thereby requires a different technology for generating the perforation structure therein. Conventional methods of perforating the thicker carrier plates utilize electron beam or laser boring which is directed at a carrier plate which is already metallized on both sides. This results, however, in the creation of control holes which have no metallization on their respective walls so that during operation charge accumulates on the hole walls which impairs the control afforded by the control plate by preventing or limiting the passage of other charge carriers through the holes.